Abstract:

A single crystal semiconductor including a Wheatstone bridge circuit
formed of an impurity diffusion layer whose longitudinal direction is
aligned with a particular crystal orientation is connected to a rotating
body. A rotating body dynamic quantity measuring device and a system
using the measuring device are fatigue- and corrosion-resistant because
of the single crystal semiconductor used and are not easily affected by
temperature variations because of the bridge circuit considering a single
crystal anisotropy.

Claims:

1. A rotating body dynamic quantity measuring device, said dynamic
quantity measuring device comprising:a Wheatstone bridge circuit having
strain sensors and dummy resistors on a [001] surface of a single crystal
silicon substrate, whereinsaid strain sensors each comprising an area
having p type impurity diffusion layer in the silicon substrate and a
longitudinal direction thereof is the same direction as a <110>
direction of the silicon substrate, said dummy resistors each comprising
an area having p type impurity diffusion layer in the silicon substrate
and a longitudinal direction thereof is at 90 degrees to the longitudinal
direction of said strain sensor, anda <100> crystal axis of said
single crystal silicon substrate is substantially parallel to a rotating
axis of said rotating body.

2. A rotating body having a dynamic quantity measuring device, said
dynamic quantity measuring device comprising:a Wheatstone bridge circuit
having strain sensors and dummy resistors on a [001] surface of a single
crystal silicon substrate, whereinsaid strain sensors each comprising an
area having n type impurity diffusion layer in the silicon substrate and
a longitudinal direction thereof is the same direction as a <100>
direction of the silicon substrate, said dummy resistors each comprising
an area having n type impurity diffusion layer in the silicon substrate
and a longitudinal direction thereof is at 90 degrees to the longitudinal
direction of said strain sensor, anda <110> crystal axis of said
single crystal silicon substrate is substantially parallel to a rotating
axis of said rotating body.

3. A rotating body having a dynamic quantity measuring device said dynamic
quantity measuring device comprising:a Wheatstone bridge circuit having
strain sensors and dummy resistors on a [001] surface of a single crystal
silicon substrate, whereinsaid strain sensors each comprising an area
having p type impurity diffusion layer in the silicon substrate and a
longitudinal direction thereof is the same direction as a <110>
direction of the silicon substrate, said dummy resistors each comprising
an area having p type impurity diffusion layer in the silicon substrate
and a longitudinal direction thereof is at 90 degrees to the longitudinal
direction of said strain sensor, anda <100> crystal axis of said
single crystal silicon substrate substantially matches the
circumferential direction of said rotating body.

4. A rotating body having a dynamic quantity measuring device, said
dynamic quantity measuring device comprising:a Wheatstone bridge circuit
having strain sensors and dummy resistors on a [001] surface of a single
crystal silicon substrate, whereinsaid strain sensors each comprising an
area having n type impurity diffusion layer in the silicon substrate and
a longitudinal direction thereof is the same direction as a <100>
direction of the silicon substrate, said dummy resistors each comprising
an area having n type impurity diffusion layer in the silicon substrate
and a longitudinal direction thereof is at 90 degrees to the longitudinal
direction of said strain sensor, anda <110> crystal axis of said
single crystal silicon substrate substantially matches the
circumferential direction of said rotating body.

5. A rotating body dynamic quantity measuring system comprising:A dynamic
quantity measure device comprising a Wheatstone bridge circuit having
strain sensors and dummy resistors on a [001] surface of a single crystal
silicon substrate, wherein said strain sensors each comprising an area
having p type impurity diffusion layer in the silicon substrate and a
longitudinal direction thereof is the same direction as a <110>
direction of the silicon substrate, said dummy resistors each comprising
an area having p type impurity diffusion layer in the silicon substrate
and a longitudinal direction thereof is at 90 degrees to the longitudinal
direction of said strain sensor;a conversion circuit for converting a
measured dynamic quantity into electromagnetic information;an antenna for
transmitted and receiving electromagnetic information; anda receiving
circuit for receiving electromagnetic information via said
antenna;wherein a <100> crystal axis of said single crystal silicon
substrate is substantially parallel to a rotating axis of said rotating
body.

6. A rotating body dynamic quantity measuring system comprising:a dynamic
quantity measuring device comprising a Wheatstone bridge circuit having
strain sensors and dummy resistors on a [001] surface of a single crystal
silicon substrate, wherein said strain sensors each comprising an area
having n type impurity diffusion layer in the silicon substrate and a
longitudinal direction thereof is the same direction as a <100>
direction of the silicon substrate, said dummy resistors each comprising
an area having n type impurity diffusion layer in the silicon substrate
and a longitudinal direction thereof is at 90 degrees to the longitudinal
direction of said strain sensor;a conversion circuit for converting a
measured dynamic quantity into electromagnetic information;an antenna for
transmitting and receiving electromagnetic information;a receiving
circuit for receiving electromagnetic information via said
antenna;wherein a <110> crystal axis of said single crystal silicon
substrate is substantially parallel to a rotating axis of said rotating
body.

7. The rotating body dynamic quantity measuring device according to claim
1, wherein a visible marking representing a rotating axial direction of
said rotating body is provided on an element forming surface of said
single crystal silicon substrate.

8. A rotating body according to claim 3, wherein a visible marking
representing a circumferential direction of said rotating body is
provided on an element forming surface of said single crystal silicon
substrate.

9. The rotating body dynamic quantity measuring system according to claim
5, further comprising:an amplification conversion circuit for amplifying
signals from said Wheatstone bridge circuit and converting them into
digital signals;a transmission circuit for transmitting the converted
digital signals to an outside of the substrate; anda power supply circuit
for supplying as electricity an electromagnetic wave energy received from
outside the substrate.

10. The rotating body dynamic quantity measuring system according to claim
5, further comprising:a conversion circuit for amplifying signals from
the Wheatstone bridge circuit and converting them into digital signals;a
transmission circuit for transmitting the converted digital signals to an
outside of the substrate; anda power supply circuit for supplying
electricity to these circuits, the electricity being derived from at
least one of a sunlight, a temperature difference, an induced
electromotive force and a batter received from outside the substrate.

11. The rotating body dynamic quantity measuring system according to claim
5, wherein said antenna is wound around more than half a circumference of
said rotating body.

12. The rotating body dynamic quantity measuring system according to claim
5, further comprising a receiving antenna being arranged to cover more
than half a circumference of said rotating body.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application is a Continuation application of application Ser.
No. 11/352,210, filed Feb. 13, 2006, which claims priority from Japanese
patent application JP 2005-035376, filed on Feb. 14, 2005, the contents
of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002]The present invention relates to a measuring system to detect
dynamic quantities of a rotating body.

[0003]Dynamic quantities of a rotating body, particularly torques, have
conventionally been measured by attaching a wire strain gauge to the
rotating body and measuring a change in a resistance of a fine metal wire
of the gauge. However, since a thin film easily develops a high cyclic
fatigue, it is difficult for the wire strain gauge to maintain
reliability for a long period when used in applications that cause high
cyclic deformations, such as measuring strains and torques of rotating
shafts. That is, the wire strain gauge has not been able to be used in
applications that affect human lives and thus require very high
reliability, such as automotive drive axels. Further, in forming a
Wheatstone bridge for temperature correction four wire strain gauges need
to be attached and their possible peeling and damage pose a problem of a
degraded reliability. Also since a metal thin film is easily corroded,
the wire strain gauges could not be used for a long period under
corrosive environments or environments containing water.

[0004]Further, in measuring torques of a rotating body some provisions
have conventionally been made, such as picking up a detected value of the
wire strain gauges through wired slipping or preparing circuits including
power supply, amplifier and transmission unit and transmitting the
detected value wirelessly. This, however, tends to make the device
complex, large and heavy. When it is attached to a shaft, the device can
easily fall because of an increased centrifugal force acting on it. Since
shafts easily deflect, various corrective measures, including
re-establishing a balance, need to be taken. That is, although it is
possible to take time and labor to perform test measurements using the
wire strain gauges, they cannot safely be used for applications that
require reliability. See JP-A-6-301881 for reference.

[0005]The present invention therefore provides rotating body dynamic
quantity measuring system and device capable of restraining some of the
problems described above.

SUMMARY OF THE INVENTION

[0006]To solve the above problems, a rotating body dynamic quantity
measuring device using a semiconductive single crystal impurity-diffused
layer is placed on a rotating body.

[0007]With this invention, since a semiconductive single crystal is used,
the device is not fatigued by a high cyclic load. It is therefore
possible to secure a sufficient reliability for a long period of use.
Further, since the device is formed of a single crystal and has no grain
boundary, it is not corroded under a corrosive environment, allowing for
a highly reliable measurement.

[0008]Further, since the rotating body dynamic quantity measuring device
using a single crystal semiconductor is very small and light in weight,
if it is attached to a rotating body, it is subjected to only a small
centrifugal force resulting from its own mass and thus requires no
special high-strength jointing method, which in turn improves
reliability. The single crystal semiconductor in particular can be
manufactured into a very small size with high precision by using the
semiconductor manufacturing technique. Therefore, there is no need for a
process to re-establish a shaft balance after the measuring device is
mounted.

[0009]As for details of this invention, the following descriptions mainly
concern an example case in which a silicon single crystal is used. It is
noted, however, that any semiconductor crystal can be similarly applied
as long as it has a diamond structure.

[0010]This invention can provide a rotating body dynamic quantity
measuring device and a rotating body dynamic quantity measuring system
capable of contributing to solving some of the above problems.

[0011]Other objects, features and advantages of the invention will become
apparent from the following description of the embodiments of the
invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic view of a measuring system as one embodiment
of this invention.

[0013]FIG. 2 is a schematic view of a rotating body dynamic quantity
measuring device in the embodiment of this invention.

[0014]FIG. 3 is a schematic view of the measuring system in the embodiment
of this invention.

[0015]FIG. 4 is a schematic view of the rotating body dynamic quantity
measuring device in the embodiment of this invention.

[0016]FIG. 5 is a schematic view of the measuring system in the embodiment
of this invention.

[0017]FIG. 6 is a schematic diagram showing a working principle for torque
measurement.

[0020]FIG. 9 is a schematic diagram showing a relation among a dispersion
layer arrangement in the rotating body dynamic quantity measuring device,
a crystal axis orientation and coordinate axes in the embodiment of this
invention.

[0021]FIG. 10 is a schematic diagram showing another relation among a
dispersion layer arrangement in the rotating body dynamic quantity
measuring device, a crystal axis orientation and coordinate axes in the
embodiment of this invention.

[0022]FIG. 11 is a schematic diagram showing still another relation among
a dispersion layer arrangement in the rotating body dynamic quantity
measuring device, a crystal axis orientation and coordinate axes in the
embodiment of this invention.

[0023]FIG. 12 is a schematic diagram showing a further relation among a
dispersion layer arrangement in the rotating body dynamic quantity
measuring device, a crystal axis orientation and coordinate axes in the
embodiment of this invention.

[0024]FIG. 13 is a schematic diagram showing a further relation among a
dispersion layer arrangement in the rotating body dynamic quantity
measuring device, a crystal axis orientation and coordinate axes in the
embodiment of this invention.

[0025]FIG. 14 is a schematic diagram showing a further relation among a
dispersion layer arrangement in the rotating body dynamic quantity
measuring device, a crystal axis orientation and coordinate axes in the
embodiment of this invention.

[0026]FIG. 15 is a schematic diagram showing how the rotating body dynamic
quantity measuring device is bonded according to the diffusion layer
arrangement in the embodiment of this invention.

[0027]FIG. 16 is a schematic diagram showing how the rotating body dynamic
quantity measuring device is bonded according to the diffusion layer
arrangement in the embodiment of this invention.

[0028]FIG. 17 is a schematic diagram showing how the rotating body dynamic
quantity measuring device is bonded according to the diffusion layer
arrangement in the embodiment of this invention.

[0029]FIG. 18 is a schematic diagram showing how the rotating body dynamic
quantity measuring device is bonded according to the diffusion layer
arrangement in the embodiment of this invention.

[0030]FIG. 19 is a schematic diagram showing a relation between an outline
geometry of a single crystal silicon and a sensitivity in this invention.

[0031]FIG. 20 is a schematic diagram showing a relation between an outline
geometry of the single crystal silicon and a sensitivity in this
invention.

[0032]FIG. 21 is a schematic view showing an example of marking formed on
the single crystal silicon in this invention.

[0033]FIG. 22 is a schematic view showing another example of marking
formed on the single crystal silicon in this invention.

[0034]FIG. 23 is a schematic view showing an example of marking formed on
the rotating body dynamic quantity measuring device of this invention.

[0035]FIG. 24 is a schematic view showing another example of marking
formed on the rotating body dynamic quantity measuring device of this
invention.

[0036]FIG. 25 is a schematic view showing a measuring system as one
embodiment of this invention.

[0037]FIG. 26 is a schematic view showing a measuring system as another
embodiment of this invention.

[0038]FIG. 27 is a schematic view showing a measuring system as a further
embodiment of this invention.

[0039]FIG. 28 is a schematic view showing a measuring system as a further
embodiment of this invention.

[0040]FIG. 29 is a schematic diagram showing how the rotating body dynamic
quantity measuring device is bonded according to the diffusion layer
arrangement in the embodiment of this invention.

[0041]FIG. 30 is a schematic diagram showing how the rotating body dynamic
quantity measuring device is bonded according to the diffusion layer
arrangement in the embodiment of this invention.

[0042]FIG. 31 is a schematic diagram showing how the rotating body dynamic
quantity measuring device is bonded according to the diffusion layer
arrangement in the embodiment of this invention.

[0043]FIG. 32 is a schematic diagram showing how the rotating body dynamic
quantity measuring device is bonded according to the diffusion layer
arrangement in the embodiment of this invention.

DESCRIPTION OF THE EMBODIMENTS

[0044]Now, embodiments of this invention will be described in detail by
referring to the accompanying drawings.

Embodiment 1

[0045]FIG. 1 shows a construction of a rotating body dynamic quantity
measuring system in a first embodiment of this invention. A rotating body
dynamic quantity measuring device 101 is installed on a surface of a
rotating shaft 12 to measure a torque of the rotating shaft 12 as the
shaft 12 rotates about a rotating center 14. The rotating body dynamic
quantity measuring device is formed of a single crystal silicon shaped
like a square chip which measures several hundred microns to several
millimeters in one side and ten microns to several hundred microns in
thickness. A back of an element forming surface or a diffusion layer is
bonded to the rotating shaft 12 to measure its strains. Normally, in
measuring the torque of the rotating shaft, a strain gauge formed of a
metal foil is used. However, the metal foil used in the strain gauge has
a short fatigue life. So when attached to a rotating shaft that undergoes
high cycle deformations, the metal foil cannot withstand a long period of
use. A semiconductor, represented by silicon, has a significantly large
yield strength compared with that of common metal foil strain gauges and
thus, when subjected to the same deformation, produces only small plastic
deformations, exhibiting a significantly long fatigue life for high cycle
deformations. The semiconductor therefore has an advantage of being able
to perform the torque measurement stably for a long period. Among strain
sensors using a semiconductor there are those using a polycrystalline
silicon. The polycrystalline silicon has many crystal grain boundaries
therein at which environmental corrosions easily occur, degrading the
measurement accuracy and causing wire breaks. When a single crystal
semiconductor is used for the rotating body dynamic quantity measuring
device, since it contains no grain boundary, the effects of environmental
corrosions at grain boundaries can be eliminated, assuring an excellent
reliability over a long period of use. As the single crystal
semiconductor, a single crystal silicon is most desirable because of its
advantages of good matching with other electric circuits, a large
destructive strength and low cost.

[0046]The rotating shaft with a torque measuring function is characterized
in that a single crystal semiconductor chip is used for a torque
measuring sensor and that an impurity diffusion layer that constitutes a
torque measuring element is formed on a silicon substrate 2. FIG. 2 shows
the rotating body dynamic quantity measuring device 101 of this
invention. Here is shown an example case where a single crystal silicon
substrate 2 is used as the single crystal semiconductor substrate. On the
single crystal semiconductor substrate 2 constituting the rotating body
dynamic quantity measuring device 101, there is formed a torque sensor 1
that utilizes at least a piezoresistive effect. A back of the substrate,
opposite the face where the torque sensor 1 is formed, constitutes a
bonding surface 3 attached to the rotating shaft 12. The bonding surface
3 and the rotating shaft 12 are preferably bonded together using an
adhesive. But they may be held together by jointing or fitting. Although
the bonding is preferably done over the entire back surface, a part of
the back surface, such as chip ends, may be left unbonded and still the
similar effect can be produced though with a slightly increased measuring
error. While in this embodiment the back surface opposite the element
forming surface is made a bonding surface, it is also possible to use the
element forming surface for bonding. In that case the measuring accuracy
improves because the element forming surface is closer to the rotating
shaft 12. The rotating body dynamic quantity measuring device 101 may
comprise, as shown in FIG. 1, a torque sensor 1 and pads 4 wired to the
torque sensor 1 on the silicon substrate 2, or may comprise, as shown in
FIG. 3, a power supply 5, an amplifier 6, an A/D converter, an analog
circuit 8, a communication control unit 9 and an antenna 10 and perform
information transfer to and from the outside circuit wirelessly. In this
case, the power supply 5 may be a battery or self-generate using
electromagnetic waves. The wireless communication with the external
circuits eliminates the need for wiring to and from the outside and thus
enables the measurement of rotating body dynamic quantities to be
performed without interfering with the rotating body motion. In the case
where the rotating body dynamic quantity measuring device 101 of FIG. 3
operates its circuit by using electromagnetic wave energy from outside,
there is no need to provide a separate power supply unit, substantially
reducing its weight, giving rise to an advantage that when the measuring
device is mounted to the rotating shaft 12, a rotation balance will not
be destroyed. Further, in the rotating body dynamic quantity measuring
device 101 shown in FIG. 3, if an energy storage unit such as a battery
is provided, a large instantaneous power can be produced, allowing the
communication distance to be increased. The antenna 10 may be installed
on the silicon substrate 2 or, as shown in FIG. 4, outside the silicon
substrate 2. When the antenna is installed outside, an area enclosed by
the antenna can be increased, making it possible to increase the
communication distance. Further, as shown in FIG. 5, a highly permeable
sheet 31 is placed between the antenna 10 and the rotating shaft 12 to
allow for communication with outside even if the rotating shaft 12 is a
metal. In this case, since the highly permeable sheet 31 is not
interposed between the silicon substrate 2 and the rotating shaft 12, the
silicon substrate 2 is directly attached to the rotating shaft 12
allowing for a highly precise torque measurement. As described above,
different configurations--one with the torque sensor placed on the
silicon substrate, one with the torque sensor, power supply 5, amplifier
6, A/D converter, analog circuit 8, communication control unit 9 and
antenna 10 installed on the silicon substrate, and one with the torque
sensor 1, power supply 5, amplifier 6, A/D converter, analog circuit 8
and communication control unit 9 installed on the silicon substrate and
with the antenna 10 installed outside--have different advantages. These
are treated as the rotating body dynamic quantity measuring device 101 in
the following descriptions of this invention.

[0047]When a torque is produced in a rotating shaft, a difference in
rotating degree occurs between the shaft ends, creating a shearing stress
τ in the shaft, as shown in FIG. 6. Thus, the torque produced in the
rotating shaft can be measured by detecting the shearing stress τ.

[0048]Silicon has a phenomenon called a piezoresistive effect in which a
resistance of the silicon changes when subjected to stresses. Silicon has
a significantly large resistance and thus, as shown in FIG. 7, a stress
can be measured by doping the silicon with impurities to form an impurity
diffused layer, applying a voltage in its longitudinal direction, and
measuring a change in electric current when a stress is produced.
Further, since the resistance of the impurity diffusion layer is strongly
influenced by temperature variations, a temperature variation correction
circuit is required. Normally, in measuring strains using a strain gauge,
a Wheatstone bridge circuit shown in FIG. 8 is used as a temperature
compensation circuit. In that case, the Wheatstone bridge circuit is
usually constructed of an active resistor sensitive to the strains and a
dummy resistor insensitive to the strains, with the active resistor
installed on a strain measuring point and the dummy resistor at an
isolated point where it is not affected by the strains.

[0049]However, if the Wheatstone bridge circuit is used in the rotating
body dynamic quantity measuring device 101 of this invention, all the
resistors must be arranged on the silicon substrate 2, in which case all
the resistors are subjected to strains, making it impossible for the
bridge circuit to perform its function correctly. In the case of the
metal foil strain gauge, a resistance change results from a change in
cross section of the resistor caused by a strain, so the strain gauge has
a sensitivity only in the longitudinal direction of the resistor.
However, in the case of the piezoresistive effect of silicon, a specific
resistance changes when the resistor is strained and its magnitude is
greater than the resistance change caused by the change in
cross-sectional area of the resistor. This means that the strain gauge
has a large sensitivity in other than the longitudinal direction. That
is, because the strain sensitivity cannot be canceled by using the
resistor geometry, a problem remains.

[0050]The construction of a bridge circuit of this invention that can
solve this problem is shown in FIG. 9. FIG. 9 represents the bridge
circuit using four resistors of p-type diffusion. The Wheatstone bridge
circuit, as described earlier, is required to have an active resistor
sensitive to a dynamic quantity to be measured and a dummy resistor with
no sensitivity or which produces an output opposite in sign to that of
the active resistor. That is, the bridge circuit requires an output
difference between the active resistor and the dummy resistor. The larger
the output resistance, the greater the sensitivity of the output of the
bridge circuit. As described earlier, silicon has a so-called
piezoresistive effect in which a natural resistance changes when the
silicon is subjected to strains. Further, in the case of a single crystal
silicon, the piezoresistive effect has an orthogonal anisotropy that
depends on the crystal orientation. That is, by changing a relationship
among the silicon crystal orientation, the arrangement of diffused
resistors and a coordinate system that functions as a reference for
strains, the resistance change with respect to strains can be
manipulated. In FIG. 9, of the four resistors of p-type impurity
diffusion layer making up the Wheatstone bridge circuit, one pair of
opposing resistors is arranged so that its longitudinal direction lies in
a [-110] direction of the single crystal silicon and the other pair is
arranged so that its longitudinal direction lies in a [110] direction,
rotated 90 degrees from the [-110] direction. That is, the Wheatstone
bridge circuit is so constructed that lines connecting the ends 102 of
each of half the resistors making up the Wheatstone bridge circuit lie
nearly in the same direction as a <110> direction of the single
crystal semiconductor but almost perpendicular to those lines connecting
the ends of each of the remaining half of the resistors making up the
Wheatstone bridge circuit. Although the first half of the resistors are
preferably set almost rectangular to the remaining half, the similar
effect can be produced as long as the two groups of resistors intersect
each other at an angle of between 45 degrees and 135 degrees. Further, as
shown in FIG. 16, a reference coordinate system for strain is arranged so
that its xy coordinate axes, perpendicular to and parallel to the
rotating axis, are in a direction almost 45 degrees in rotation from the
[-110] direction of the silicon crystal. While the side of the chip is
depicted in FIG. 16 to be parallel to the <110>, if the direction
of the diffusion resistor is <110>, the side of the chip may be set
parallel to <100>. In the embodiments of FIG. 15 and FIG. 16, the
diffusion resistors parallel to the [-110] direction have a large
sensitivity to the shearing strain τxy but almost none for other
strains.

[0051]The resistors parallel to the [110] direction have a large
sensitivity for only τxy and produce an output opposite in sign
to that of the resistors oriented in the [-110] direction. That is, the
building the Wheatstone bridge circuit in the arrangement of FIG. 9
offers an advantage of being able to measure only the shearing strain
τxy with four times the sensitivity. In a strain gauge using
metal fine wires, if there are stresses other than τxy, their
influences result in resistance changes. In the rotating body dynamic
quantity measuring device 101, their influences are very small, assuring
a highly precise measurement of torque. This advantage, too, is obtained
because the rotating body dynamic quantity measuring device 101 is formed
of a single crystal silicon and is bonded considering the crystal axis
orientation. By arranging this bridge circuit so that the bridge circuit
is symmetrical about its center four times on the silicon substrate, as
shown in FIG. 9 and FIG. 11, the relationship between the adjoining
resistors can be made equal for all of the four resistors. In forming a
diffusion layer of an arbitrary geometry on silicon, etching is used to
form that geometry on the mask. To make four resistances equal requires
forming the same geometries on the mask for all the resistors to be
formed. During an etching process the density of etching gas on the mask
changes depending on the surrounding environment, greatly affecting the
accuracy of the geometry of the resistors being formed. By forming the
diffused resistors in the layout of FIG. 9 and FIG. 11, the influences of
the surrounding environment to which all the four resistors are subjected
can be made equal, so the mask for the four resistors can be etched in
the same geometry. Therefore, when the impurity diffusion layer is
formed, it is possible to make the resistances of the four resistors
equal, reduce an offset of the Wheatstone bridge circuit and thereby
assure a highly precise measurement of strains. Another arrangement in
which, as shown in FIG. 10, two resistors are interposed between the
other opposing resistors, offers an advantage of being able to reduce an
area occupied by the bridge circuit in a case where an area in which to
arrange the bridge circuit is limited, as when the silicon substrate 2 is
made as small as possible to manufacture a infinitesimally small,
rotating body dynamic quantity measuring device 101 or when other
circuits such as a wireless communication circuit are also mounted on the
silicon substrate 2 as described above.

[0052]Although an example case of p-type diffusion layer has been taken up
to explain the method of its arrangement, the similar effect can be
produced if the diffusion layer is an n-type. The rotating body dynamic
quantity measuring device 101 using the n-type diffusion layer has an
advantage of a high sensitivity. When the resistors making up the bridge
circuit is an n-type diffusion layer, a pair of opposing resistors is so
arranged that, as shown in FIG. 12, its longitudinal direction lies in
the [100] direction of the silicon single crystal and the remaining pair
of resistors is so arranged that its longitudinal direction lies in [010]
direction, which is 90 degrees in rotation from the [100] direction. That
is, the resistors are arranged so that lines connecting the ends of each
of half the resistors making up the Wheatstone bridge circuit lie nearly
in the same direction as a <100> direction of the single crystal
semiconductor but almost perpendicular to those lines connecting the ends
of each of the remaining half of the resistors making up the Wheatstone
bridge circuit. Although the first half of the resistors are preferably
set almost rectangular to the remaining half, the similar effect can be
produced as long as the two groups of resistors intersect each other at
an angle of between 45 degrees and 135 degrees. Further, as shown in FIG.
17 and FIG. 18, the reference coordinate system for strains is arranged
so that its xy coordinate axes, perpendicular to and parallel to the
rotating axis, lie in a direction almost 45 degrees in rotation from the
crystal orientation of [100]. In FIG. 17 and FIG. 18, although the sides
of the chip are shown to be parallel to <110>, if the direction of
the diffusion resistors is <100>, the sides of the chip may be set
parallel to <100>. In that case, since the elements other than the
diffusion layer can be formed parallel to and perpendicular to
<100>, they are not easily affected by the strains. In the
embodiment of FIG. 17, the resistors parallel to the [100] direction have
a high sensitivity for the shearing strain τxy but almost none
for other strains. The resistors parallel to the [010] direction also
have a high sensitivity for only the shearing strain τxy but
produce an output opposite in sign to the output of the resistors
arranged in the [100] direction. That is, by forming a Wheatstone bridge
circuit in the arrangement of FIG. 9, a sensor can be manufactured that
can measure only the shearing strain τxy with high precision. In
the case of n-type diffusion layer, too, variations of the resistor
geometries during the mask fabrication can be eliminated by arranging the
four resistors so that the 4-time symmetric axis of the bridge circuit
lies at their center, as shown in FIG. 12 and FIG. 14, as in the case of
p-type diffusion layer. This in turn reduces an offset of the bridge
circuit. Further, when the resistors are arranged as shown in FIG. 13,
there is an advantage that the area occupied by the bridge circuit can be
reduced.

[0053]In the above arrangement of the impurity diffusion layer that works
as resistors, the description that the longitudinal direction lies in the
[100] direction means that the direction of a line connecting two via
electrodes connected to the resistor lies close to the [100] direction
and that, when viewed macroscopically, the [100] direction matches the
longitudinal direction. In the path connecting the two via electrodes,
the geometry of the diffusion layer may be formed zigzag to increase its
resistance. This applies to both of the n-type impurity and p-type
impurity.

[0054]Although the rotating body dynamic quantity measuring device
described above resembles the prior art used in pressure sensors when we
look at only the crystal orientation with respect to the longitudinal
direction of the diffusion layer, its construction and working principle
differ entirely from those of the prior art. In the pressure sensor, a
hole is formed in a silicon substrate to form a diaphragm and a
deformation of the diaphragm when subjected to a pressure is detected by
a strain sensor formed on the surface of the silicon substrate. That is,
local deformations of the diaphragm due to pressure are detected by two
of the four diffusion layer resistors making up the Wheatstone bridge
circuit. The other two diffusion layer resistors are used as dummies and
arranged at a location and in a direction where they are not easily
affected by the deformation of the diaphragm. In this rotating body
dynamic quantity measuring device, however, since the strain fields to
which the four diffusion layer resistors in the silicon substrate are
subjected are theoretically the same, it is difficult to manufacture
dummy diffusion layer resistors by utilizing a difference in local
deformation as in the pressure sensor. The inventors of this invention
have found that the above arrangement can extract only a shearing stress
well only when measuring a torque of a rotating shaft. This has led us to
this invention. In the case of this invention, unlike the pressure
sensor, it is desired that a uniform strain field be generated in the
silicon substrate. Thus, if there is a hole larger in width than the
shorter side of the diffusion layer, as in the pressure sensor, in the
back of the silicon substrate which is opposite the element forming
surface of the silicon substrate and which is directly or indirectly
placed in contact with an object to be measured, complex strain fields
are generated in the silicon substrate, which is not desirable. Small
undulations or holes in the back of the silicon substrate may be
conducive to an improvement in the adhesion between the object and the
measuring device, but any hole greater in depth than half the thickness
of the silicon substrate will cause complicated strain fields in the
silicon substrate. This is not desirable.

Embodiment 2

[0055]The rotating body dynamic quantity measuring device 101 of this
invention is manufactured by forming minute, thin film structures several
microns in size on the silicon substrate several millimeters square using
the semiconductor fabrication process. So it is difficult to visually
identify the diffusion layer in the rotating body dynamic quantity
measuring device 101. The sensor of this invention considers the
direction in which a strain is measured, the crystal orientation, and the
direction in which the impurity diffused resistors are arranged.
Therefore, what matters in the site of actual use of the rotating body
dynamic quantity measuring device 101 is how the device is arranged with
respect to the direction in which a strain is to be taken. So, as shown
in FIG. 21, a mark 17 is formed in the rotating body dynamic quantity
measuring device 101. FIG. 21 shows a rotating body dynamic quantity
measuring device using a bridge circuit of a p-type diffusion layer on
which an arrow is marked indicating an axial direction of the shaft. The
user can make a correct measurement of a torque generated in the rotating
shaft by arranging the rotating body dynamic quantity measuring device so
that its arrow is parallel to the center axis of the rotating shaft. The
arrow marking 17 may be formed of thin film or marked with ink or paint.
The marking may also be dots or line as well as arrow. FIG. 22 shows an
example case in which the rotating body dynamic quantity measuring device
is manufactured using an n-type impurity diffusion layer. In the figure
an arrow 17 is marked which is parallel to the direction of sides of the
silicon substrate 2. The user can take accurate measurements of torque by
arranging the rotating body dynamic quantity measuring device so that the
arrow marking on the device is parallel to the central axis of the
rotating body. As shown in FIG. 23 and FIG. 24, the arrow representing a
direction may be marked on an antenna support portion 11, such as a film,
that supports the antenna, rather than on the chip.

Embodiment 3

[0056]FIG. 25 shows a third embodiment of the rotating body dynamic
quantity measuring system according to this invention. FIG. 25
schematically shows the rotating shaft 12 as seen from the end, on the
circumferential surface of which is attached a plurality of rotating body
dynamic quantity measuring devices 101 with a wireless communication
function. Radio waves transmitted from the rotating body dynamic quantity
measuring devices 101 are received by a receiving antenna 18 and
converted by a receiving unit 19 into strain and torque values. When the
rotating shaft 12 is formed of a conductive body such as metal, radio
waves do not easily travel to the far side of the shaft. To cope with
this problem, this embodiment has a plurality of rotating body dynamic
quantity measuring devices 101 attached to the circumferential surface of
the rotating shaft to enable measurement at all times. This embodiment
offers an advantage that there is no area where strain measurements
cannot be taken because of the inability to receive radio waves.

[0057]FIG. 26 shows another rotating body dynamic quantity measuring
system according to this invention. This embodiment is characterized in
that the receiving antenna 18 encircles the rotating shaft 12. The radio
waves from the rotating body dynamic quantity measuring device 101 can be
received by the receiving antenna 18 no matter where the measuring device
101 is located. This embodiment offers an advantage that there is no area
where strain measurements cannot be taken because of the inability to
receive radio waves. As shown in FIG. 27, the antenna 10 of the measuring
device 101 may also be attached to the entire circumferential surface of
the rotating shaft 12. In that case, there is an advantage of
facilitating the mounting of the receiving antenna.

[0058]FIG. 17 shows still another rotating body dynamic quantity measuring
system according to this invention. This embodiment represents a case
where the rotating body is a disk and its shearing strain is measured.
The shearing strain of the disk can be measured by the rotating body
dynamic quantity measuring device 101 attached to the surface of the
disk. In addition to the advantage in the torque measurement of a
rotating shaft, this embodiment offers another advantage that since the
measuring device 101 is very small, measurements can also be taken if an
area of the disk is small. This embodiment is particularly effective
where a rotating disk 20 is applied a frictional force by pressing
objects 21 against the disk to block its motion. When, for example, the
measuring device 101 has a pattern of p-type diffusion layer of FIG. 11,
the measuring device is arranged so that the circumferential direction of
the disk almost matches the <100> crystal axis of the silicon
crystal as shown in FIG. 29 and FIG. 30 and that the longitudinal
direction of the diffusion layer is aligned with the <110>
direction. If the measuring device 101 has a pattern of n-type diffusion
layer of FIG. 12, the measuring device is arranged so that the
circumferential direction of the disk almost matches the <110>
crystal axis of the silicon crystal as shown in FIG. 31 and FIG. 32 and
that the longitudinal direction of the diffusion layer is aligned with
the <100> direction.

[0059]The present invention can be applied to devices that measure torques
of rotating bodies.

[0060]Some aspects of the invention will be described in conjunction with
the description of embodiments.

[0061]Viewed from a first aspect, the present invention provides a
rotating body dynamic quantity measuring device comprising: a Wheatstone
bridge circuit formed on an element forming surface, namely, a main
surface of a single crystal semiconductor substrate, the Wheatstone
bridge circuit being constructed of resistors of a p-type impurity
diffusion layer; wherein the resistors are so arranged that lines
connecting ends of each of half the resistors making up the Wheatstone
bridge circuit lie nearly in the same direction as a <110>
direction of the single crystal semiconductor and intersect those lines
connecting ends of each of the remaining half of the resistors making up
the Wheatstone bridge circuit at an angle of between 45 degrees and 135
degrees; wherein, on a back of the single crystal semiconductor substrate
opposite the element forming surface, there is no hole greater in width
than a shorter side of the p-type impurity diffusion layer forming the
Wheatstone bridge circuit.

[0062]A second aspect of the present invention provides a rotating body
dynamic quantity measuring device comprising: a Wheatstone bridge circuit
formed on an element forming surface, namely, a main surface of a single
crystal semiconductor substrate, the Wheatstone bridge circuit being
constructed of resistors of a n-type impurity diffusion layer; wherein
the resistors are so arranged that lines connecting ends of each of half
the resistors making up the Wheatstone bridge circuit lie nearly in the
same direction as a <100> direction of the single crystal
semiconductor and intersect those lines connecting ends of each of the
remaining half of the resistors making up the Wheatstone bridge circuit
at an angle of between 45 degrees and 135 degrees; wherein, on a back of
the single crystal semiconductor substrate opposite the element forming
surface, there is no hole greater in width than a shorter side of the
n-type impurity diffusion layer forming the Wheatstone bridge circuit.

[0063]A third aspect of the present invention provides a rotating body
dynamic quantity measuring device comprising: a Wheatstone bridge circuit
formed on an element forming surface, namely, a main surface of a single
crystal semiconductor substrate, the Wheatstone bridge circuit being
constructed of resistors of a p-type impurity diffusion layer; wherein
the resistors are so arranged that lines connecting ends of each of half
the resistors making up the Wheatstone bridge circuit lie nearly in the
same direction as a <110> direction of the single crystal
semiconductor and intersect those lines connecting ends of each of the
remaining half of the resistors making up the Wheatstone bridge circuit
at an angle of between 45 degrees and 135 degrees; wherein, on a back of
the single crystal semiconductor substrate opposite the element forming
surface, there is no hole greater in depth than half the thickness of the
single crystal substrate.

[0064]A fourth aspect of the present invention provides a rotating body
dynamic quantity measuring device comprising: a Wheatstone bridge circuit
formed on an element forming surface, namely, a main surface of a single
crystal semiconductor substrate, the Wheatstone bridge circuit being
constructed of resistors of a n-type impurity diffusion layer; wherein
the resistors are so arranged that lines connecting ends of each of half
the resistors making up the Wheatstone bridge circuit lie nearly in the
same direction as a <100> direction of the single crystal
semiconductor and intersect those lines connecting ends of each of the
remaining half of the resistors making up the Wheatstone bridge circuit
at an angle of between 45 degrees and 135 degrees; wherein, on a back of
the single crystal semiconductor substrate opposite the element forming
surface, there is no hole greater in depth than half the thickness of the
single crystal substrate.

[0065]A fifth aspect of the present invention provides a rotating body
dynamic quantity measuring device according to the first aspect, further
including: an amplification conversion circuit to amplify signals from
the Wheatstone bridge circuit and convert them into digital signals; a
transmission circuit to transmit the converted digital signals to an
outside of the semiconductor substrate; and a power supply circuit to
supply as electricity an electromagnetic wave energy received from
outside the semiconductor substrate.

[0066]A sixth aspect of the present invention provides a rotating body
dynamic quantity measuring device according to the second aspect, further
including: an amplification conversion circuit to amplify signals from
the Wheatstone bridge circuit and convert them into digital signals; a
transmission circuit to transmit the converted digital signals to an
outside of the semiconductor substrate; and a power supply circuit to
supply as electricity an electromagnetic wave energy received from
outside the semiconductor substrate.

[0067]A seventh aspect of the present invention provides a rotating body
dynamic quantity measuring device according to the first aspect, further
including: a conversion circuit to amplify signals from the Wheatstone
bridge circuit and convert them into digital signals; a transmission
circuit to transmit the converted digital signals to an outside of the
semiconductor substrate; and a power supply circuit to supply electricity
to these circuits, the electricity being derived from at least one of a
sunlight, a temperature difference, an induced electromotive force and a
battery received from outside the semiconductor substrate.

[0068]An eighth aspect of the present invention provides a rotating body
dynamic quantity measuring device according to the second aspect, further
including: a conversion circuit to amplify signals from the Wheatstone
bridge circuit and convert them into digital signals; a transmission
circuit to transmit the converted digital signals to an outside of the
semiconductor substrate; and a power supply circuit to supply electricity
to these circuits, the electricity being derived from at least one of a
sunlight, a temperature difference, an induced electromotive force and a
battery received from outside the semiconductor substrate.

[0069]An ninth aspect of the present invention provides a rotating body
dynamic quantity measuring device according to any one of the first to
eighth aspects, wherein the impurity diffusion layer is configured and
arranged in nearly a four-time symmetry.

[0070]A tenth aspect of the present invention provides a rotating body
dynamic quantity measuring device according to any one of the first to
eighth aspects, wherein the impurity diffusion layer is configured and
arranged in nearly a mirror symmetry.

[0071]An eleventh aspect of the present invention provides a rotating body
dynamic quantity measuring device according to any one of the first to
tenth aspects, wherein a visible marking representing an axial direction
or circumferential direction of a rotating shaft is provided on the
element forming surface of the semiconductor substrate.

[0072]A twelfth aspect of the present invention provides a rotating body
dynamic quantity measuring device according to any one of the first to
tenth aspects, wherein a bonding portion to be attached to an object
being measured is formed on a back of the single crystal semiconductor
substrate opposite the main surface.

[0073]A thirteenth aspect of the present invention provides a rotating
body having a dynamic quantity measuring unit of a rotating body dynamic
quantity measuring device attached to a surface thereof, wherein the
dynamic quantity measuring unit includes a single crystal semiconductor
having an impurity diffusion layer formed in a surface thereof and a back
of the single crystal semiconductor opposite the surface formed with the
impurity diffusion layer is attached to the rotating body.

[0074]A fourteenth aspect of the present invention provides a rotating
body according to the thirteenth aspect, wherein the dynamic quantity
measuring unit includes a single crystal semiconductor having a p-type
impurity diffusion layer formed in a surface thereof and a <100>
direction of the single crystal semiconductor formed with the p-type
impurity diffusion layer is almost parallel to a rotating axis of the
rotating body.

[0075]A fifteenth aspect of the present invention provides a rotating body
according to the thirteenth aspect, wherein the dynamic quantity
measuring unit includes a single crystal semiconductor having an n-type
impurity diffusion layer formed in a surface thereof and a <110>
direction of the single crystal semiconductor formed with the n-type
impurity diffusion layer is almost parallel to a rotating axis of the
body.

[0076]A sixteenth aspect of the present invention provides a rotating body
attached with the rotating body dynamic quantity measuring device of the
first, third, fifth, seventh, thirteenth or fourteenth aspect, wherein a
rotating axis direction of the rotating body is almost parallel to a
<100> direction of the single crystal semiconductor.

[0077]A seventeenth aspect of the present invention provides a rotating
body attached with the rotating body dynamic quantity measuring device of
the second, fourth, sixth, eighth, thirteenth or fifteenth aspect,
wherein a rotating axis direction of the rotating body is almost parallel
to a <110> direction of the single crystal semiconductor.

[0078]A eighteenth aspect of the present invention provides a rotating
body dynamic quantity measuring system having a dynamic quantity
measuring unit of a rotating body dynamic quantity measuring device
attached to a rotating body, wherein dynamic quantity data measured by
the dynamic quantity measuring unit and converted into electromagnetic
wave information is received by an antenna and a receiving unit to detect
the dynamic quantities of the rotating body; wherein the dynamic quantity
measuring unit includes a single crystal semiconductor having an impurity
diffusion layer formed in a surface thereof and a back of the single
crystal semiconductor opposite the surface formed with the impurity
diffusion layer is attached to the rotating body.

[0079]A nineteenth aspect of the present invention provides a rotating
body dynamic quantity measuring system according to the eighteenth
aspect, wherein the dynamic quantity measuring unit includes a single
crystal semiconductor having a p-type impurity diffusion layer formed in
a surface thereof and a <100> crystal axis of the single crystal
semiconductor formed with the p-type impurity diffusion layer is almost
parallel to a rotating axis of the rotating body.

[0080]A twentieth aspect of the present invention provides a rotating body
dynamic quantity measuring system according to the eighteenth aspect,
wherein the dynamic quantity measuring unit includes a single crystal
semiconductor having a p-type impurity diffusion layer formed in a
surface thereof and a <110> crystal axis of the single crystal
semiconductor formed with the p-type impurity diffusion layer is almost
parallel to a rotating axis of the rotating body.

[0081]A twenty first aspect of the present invention provides a rotating
body dynamic quantity measuring system according to any one of the
eighteenth to twentieth aspects, wherein a plurality of rotating body
dynamic quantity measuring devices are installed on one rotating shaft.

[0082]A twenty second aspect of the present invention provides a rotating
body dynamic quantity measuring system according to any one of the
eighteenth to twentieth aspects, wherein an antenna is wound around more
than half a circumference of a rotating shaft.

[0083]A twenty third aspect of the present invention provides a rotating
body dynamic quantity measuring system according to any one of the
eighteenth to twentieth aspect, wherein a receiving antenna is arranged
to cover more than half a circumference of a rotating shaft.

[0084]A twenty fourth aspect of the present invention provides a rotating
body dynamic quantity measuring system according to the eighteenth
aspect, wherein the rotating body is a disk, the dynamic quantity
measuring unit includes a single crystal semiconductor having a p-type
impurity diffusion layer formed in a surface thereof, and a <100>
crystal axis of the single crystal semiconductor formed with the p-type
impurity diffusion layer almost matches a circumferential direction of
the disk.

[0085]A twenty fifth aspect of the present invention provides a rotating
body dynamic quantity measuring system according to the eighteenth
aspect, wherein the rotating body is a disk, the dynamic quantity
measuring unit includes a single crystal semiconductor having an n-type
impurity diffusion layer formed in a surface thereof, and a <110>
crystal axis of the single crystal semiconductor formed with the n-type
impurity diffusion layer almost matches a circumferential direction of
the disk.

[0086]It should be further understood by those skilled in the art that
although the foregoing description has been made on embodiments of the
invention, the invention is not limited thereto and various changes and
modifications may be made without departing from the spirit of the
invention and the scope of the appended claims.